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5.3 TOX1CITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 255

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FIGURE 5.32 Elements of risk assessment and risk management. (used with permission.)

to single chemicals is still far from complete, much greater difficulties are
encountered in assessing the risks of multiple exposures.

5.3.2 Exposure to Chemical Substances

Among the 10 million known chemical compounds, there are some 50 000
which are in common use. Workers are usually exposed to several agents si-
multaneously (their interactions are considered in section 5.3.4.2). In addi-
tion, many impurities in workplace air are inherently complex mixtures,
which may consist of hundreds of different compounds. Mineral oils and
wood dusts are examples of common complex mixtures.

5.3.2.1 Characterization of Exposures
Indoor and Outdoor Exposure to Pollutants
Occupational and environmental exposure to chemicals can take place
both indoors and outdoors. Occupational exposure is caused by the chemicals
that are used and produced indoors in industrial plants, whereas nonoccupa-
tional (and occupational nonindustrial) indoor exposure is mainly caused by
products. Toluene in printing plants and styrene in the reinforced plastic indus-
try are typical examples of the two types of industrial occupational exposures.
Products containing styrene polymers may release the styrene monomer into
indoor air in the nonindustrial environment for a long time. Formaldehyde is
another typical indoor pollutant. The source of formaldehyde is the resins used
in the production process. During accidents, occupational and environmental
exposures may occur simultaneously. Years ago, dioxin was formed as a by-
product of production of phenoxy acid herbicides. An explosion in a factory in